1. Field of the Invention
The present invention relates to solid-state switches and more particularly to solid-state switches whose operation is controllable by an integrated circuit.
2. Discussion of the Related Art
A controllable switch may be designed for connection in a circuit in series with a load whose current will be adjusted. A practical problem of such an arrangement is that the control integrated circuit should be supplied with a specific low voltage supply (in some examples 5 to 15 volts). Thus, it may be desired to form units which each include the switch and a power supply for the integrated circuit, which significantly simplifies the mounting of these switches and of their control integrated circuit.
FIG. 1 illustrates a circuit which includes a voltage source S supplying a load L in series with a switching unit 1. The switching unit 1 is controlled by an integrated circuit IC, and includes the switch SW connected between terminals A1 and A2, and output terminals 2 and 3 to supply the integrated circuit. A specific problem raised by such an arrangement is that, when switch SW is turned-on, the voltage between the terminals of switch SW is low or zero and therefore the voltage across terminals 2 and 3 may be too low to provide power to the integrated circuit IC. To avoid this drawback, it has been devised to connect a storing capacitor C between terminals 2 and 3.
Such devices satisfactorily operate but require a high-value capacitor C for long-lasting switching-on of the switch SW. Indeed, if source S corresponds to the a.c. voltage of the mains or to the rectified mains voltage, the case in which the control of the switch causes its closing during several periods of the mains voltage must be provided for.
To solve this problem, a switch has been associated with a low-voltage supply circuit designed so that, when a switch-on order is transmitted to the switch, this order is inhibited as long as the voltage across the switch has not reached the desired threshold supply voltage. Thus, a storing capacitor can be charged again at the beginning of each half-period of the voltage applied and thus can be a small size capacitor.
Such a circuit is disclosed in French patent 2222801. However the implementation of such a circuit implies the use and the connection of a large number of components.